Side emitting optical fibers or fiber bundles that are illuminated by primary optical sources placed only at the ends of the fibers are recognized as practical and convenient methods for distributed illumination. They provide inherently safe illumination that is continuous and flexible, since the illumination is distributed along the full length of the fibers or fiber bundles. These sources require no electrical power to be provided within the structure of the fiber or fiber bundle itself, since the primary optical sources that do require electrical supply are located only at the end or ends of the side emitting fibers or fiber bundles.
Side emitting fibers or fiber bundles can provide high intensity light at peak eye response, as well as light of other colors as required. They are particularly appropriate for use in hazardous environments, for example in chemical or oil refining plants, mines, wellheads, and oil-rig platforms, where illumination methodologies involving the supply of electrical power within the hazardous environments can lead to risk of explosions. They also lend themselves to use in underwater environments, for example, subsea and any inland water including lakes, rivers, lochs, harbors, docks, canals and all other types of waterways, including in aqua-culture, as well as in many other environmentally challenging situations. In addition, they are ideal for providing egress/guide-path lighting and safety lighting, for example for illuminating clear paths to exits. This results from the distributed and continuous nature of the source along the length of the fiber or fiber bundle. Furthermore, such sources can also serve the dual purpose of illumination and communication, where information is dispersed through appropriate modulation of the emitted light.
Side emitting fibers or fiber bundles are used with optical sources, which generally are associated with electrical/electronic components. Using such devices in hazardous/challenging environments can be problematic, as the environment in which the electrical/electronic/optical components forming the primary optical source are located has to be isolated from the external environment to which the side emitting fiber or fiber bundle is itself subject. Furthermore, the sealing integrity between the fiber and the electrical environments has to be sustained during installation, usage, servicing and replacement. In practice, locating and retaining the fiber relative to the primary light source can be difficult. Also, there can be problems with optimizing the coupling of radiation from the primary light source into the fiber/fiber bundle, and isolating the primary light source, including protection from dangerous environments. Efficient management of heat removal from the primary light source is a further challenge.